On-Demand Routing Protocols • Routes are established “on demand” as requested by the source • Only the active routes are maintained by each node • Channel/Memory overhead is minimized • Two leading methods for route discovery: source routing and backward learning (similar to LAN interconnection routing)
On Demand Routing - Readings • D. B. Johnson and D. A. Maltz, "Dynamic Source Routing in Ad-Hoc Wireless Networks," Mobile Computing, 1994. Charles E. Perkins and Elizabeth M. Royer. "Ad hoc On-Demand Distance Vector Routing." Proceedings of the 2nd IEEE Workshop on Mobile Computing Systems and Applications, New Orleans, LA, February 1999, pp. 90-100.
Existing On-Demand Protocols • Dynamic Source Routing (DSR) • Associativity-Based Routing (ABR) • Ad-hoc On-demand Distance Vector (AODV) • Temporarily Ordered Routing Algorithm (TORA) • Zone Routing Protocol (ZRP) • Signal Stability Based Adaptive Routing (SSA) • On Demand Multicast Routing Protocol (ODMRP)
Dynamic Source Routing (DSR) • Forwarding: source route driven instead of hop-by-hop route table driven • No periodic routing update message is sent • The first path discovered is selected as the route • Two main phases – – Route Discovery Route Discovery – Route Maintenance – Route Maintenance
DSR - Route Discovery • To establish a route, the source floods a Route Request Route Request message with a unique request ID • The Route Request packet “picks up” the node ID numbers • Route Reply message containing path information is sent • Route Reply back to the source either by – the destination, or – intermediate nodes that have a route to the destination • Each node maintains a Route Cache Route Cache which records routes it has learned and overheard over time
DSR - Route Maintenance • Route maintenance performed only while route is in use • Monitors the validity of existing routes by passively listening to acknowledgments of data packets transmitted to neighboring nodes • When problem detected, send Route Error Route Error packet to original sender to perform new route discovery
Ad hoc On-Demand Distance Vector Routing (AODV) • Primary Objectives – Provide unicast, broadcast, and multicast capability – Initiate forward route discovery only on demand – Disseminate changes in local connectivity to those neighboring nodes likely to need the information • Characteristics – On-demand route creation • Effect of topology changes is localized • Control traffic is minimized – Two dimensional routing metric: <Seq#, HopCount> – Storage of routes in Route Table
Route Table • Fields: – Destination IP Address – Destination Sequence Number – HopCount Precursor Nodes Next Hop A – Next Hop IP Address – Precursor Nodes Destination Source – Expiration Time Source • Each time a route entry is used to transmit data, the expiration time is updated to current_time + active_route_timeout
Unicast Route Discovery • Source broadcasts Route Request (RREQ) < Flags, Bcast_ID, HopCnt, Src_Addr, Src_Seq#, Dst_Addr, Dst_Seq# > Source • Node can reply to RREQ if – It is the destination, or – It has a “fresh enough” route to the destination • Otherwise it rebroadcasts the request Destination • Nodes create reverse route entry Route Request Propagation • Record Src IP Addr / Broadcast ID to prevent multiple rebroadcasts
Forward Path Setup • Destination, or intermediate node with current route to destination, unicasts Route Reply (RREP) to source Source < Flags, HopCnt, Dst_Addr, Dst_Seq#, Src_Addr, Lifetime> • Nodes along path create forward route Destination • Source begins sending data when it receives first RREP Forward Path Formation
Path Maintenance 3’ 3’ 3 1 1 Destination Destination 2 2 Source Source 4 4 • Movement of nodes not along active path does not trigger protocol action • If source node moves, it can reinitiate route discovery • When destination or intermediate node moves, upstream node of break broadcasts Route Error (RERR) message • RERR contains list of all destinations no longer reachable due to link break • RERR propagated until node with no precursors for destination is reached
GloMoSim/Qualnet Simulation Layers Control Plane Control Plane Data Plane Data Plane Application Processing Application Setup Application RTP Wrapper RCTP TCP/UDP Control Transport Wrapper Transport RSVP IP Wrapper IP/Mobile IP Routing IP VC Flow Packet Store/Forward Clustering Routing Network Handle Control Packet Store/Forward Ack/Flow Control Link Layer Clustering Frame Wrapper RTS/CTS CS/Radio Setup MAC Layer Radio Status/Setup Frame Processing Radio Propagation Model Mobility Channel
Performance Evaluation Enviroment • PARSEC simulation enviroment – 100 nodes – 1000mx1000m square area – transmission range: 100m – channel data rate: 2 Mbps – random mobility model – UDP traffic between randomly selected node pairs – cluster-token MAC layer protocol • HSR – 2 level physical partition – 1 level logical groupings, number of logical subnets varies with network size • FSR – 2 level fisheye scoping – fisheye radius is 2 hops
Control O/H vs. number of nodes Control O/H (Mbits/Cluster) 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 25 49 100 225 324 400 Number of nodes On-demand DSDV HSR FSR
Control O/H vs. Traffic Pairs
Control O/H vs. Mobility (100 pairs)
Average Delay (ms)
Location-Aided Routing (LAR) • Ko and Vaidya (Texas A & M) • Location assisted (requires GPS) • On-demand • No periodic messages • LAR works like DSR except it limits the flooded area of Route Requests Route Requests using location information
LAR (cont’d) • Scheme 1 – The source specifies a request zone which includes the source and the area where the destination may reside – Nodes within the request zone propagate Route Route Requests Requests • Scheme 2 – The source specifies the distance between itself and the destination – Nodes forward Route Requests Route Requests if their distances to the destination is less than or equal to the distance indicated by the packet
DREAM • Besagni, et al. (U of Texas, Dallas) • Location assisted (requires GPS) • Node coordinates (instead of routes) are recorded in the route table • Distance Effect : Send location updates to nearby • Distance Effect nodes more frequently • Location update frequencies are adjusted to mobility rate
DREAM (cont’d) • The source partially floods data to nodes that are in the direction of the destination • The source specifies possible next hops in the data header using location information • Next hop nodes select their own list of next hops and include the list into data header • If the source finds no neighbors in the direction of the destination or has no fresh location information of the destination, data is flooded to the entire network
Location Based Routing Simulation (LAR and DREAM) • 50 nodes; 750m X 750 m space • Free space channel propagation model • Radio with capture ability • MAC: IEEE 802.11 DCF • 10 UDP data sessions with constant bit rate
Simulation Results (cont’d) • Packet delivery ratio
Simulation Results • Number of data packets transmitted per data packet delivered
Simulation Results (cont’d) • Number of control bytes transmitted per data byte delivered
Conclusions • Conventional (wired net) routing schemes suffer of O/H, mobility and scalability limitations • Hierarchical routing reduces O/H and improves scalability (at the expense of accuracy). • On Demand routing eliminates background routing control O/H. It introduces latency; it does not well suited for QoS routing
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